Electronic components such as integrated circuit chips produce heat during operation. These components may be mounted on circuit substrates to form circuit assemblies. These assemblies are often confined within casings where convective air cooling is hampered. Cooling solutions are necessary for certain electronic components to maintain operational temperatures below a critical level, which, if reached, may damage the electronic component or reduce its efficiency or effectiveness. Thermal management devices are mounted to the electronic component to be cooled and drain heat from the component by heat conduction, heat convection or heat irradiation. Ultimately, the heat from the component is drained to the surrounding air in a forced or natural flow of air. Various cooling solutions are well known in the art. For example, a heat sink typically made of copper or aluminum can be attached to the outer surface of the electronic component with a thermal adhesive. The heat generated by the electronic component is then drained from the electronic component onto another colder heat sink by conduction. The conductive adhesive may be a thermal conductor that allows for heat transfer while offering some degree of resistance to the heat flux. The heat sink in turn transfers the heat to the surrounding air via natural or forced convection. One forced convection method includes the use of a fan placed near or on the heat sink to increase the air flow near over the heat sink. Another forced convection method includes cooling the air itself using an air-cooling system that forces movement of the convective structure within the air.
Known conductive and convective air-cooling methods, however, fail to provide adequate heat removal for certain electronic devices that use intensive heat generating components or require intense local cooling. In electronic devices, components may require cooling to lower surface temperatures to maintain the component efficiency. The surface of components may also heat unevenly, creating hot spots that, unless cooled locally, reduce the overall efficiency of the thermal management device by reducing the average temperature difference between the component surface and the device before the component surface temperature reaches a critical level. Improved efficiency of new thermal management devices for small heating components used in electronic devices is limited where the internal space between the various components is of known and recognized usefulness.
One method of cooling electronic components uses an evaporation and condensation cycle within a closed body to transfer heat from a hot surface of the body to a cold surface of the body. A volume of fluid, along with a pressurized volume of gas, is housed in a closed conductive volume called a vapor chamber. The fluid contacts a first surface of the volume at temperatures above the boiling point of the fluid at the determined pressure. The fluid absorbs the heat from the surface and evaporates. Local ebullition also creates fluidic convective movements inherently designed to further improve local heat transfer. The vapor then migrates by pressure differential to another part of the conductive volume and condenses on a second surface at a temperature below the boiling point of the fluid at the determined pressure. During condensation of the gas, heat is transferred to the second surface, effectively closing the thermal cycle and transferring heat from a hot surface to a cold surface. Water and water vapor may be used along with a neutral gas such as nitrogen when component surfaces to be cooled are located in the range of the boiling point of water at the selected air pressure. What is known in the art is the use of a simplified geometry to form vapor chambers, such as flat rectangular shapes or cylindrical tubes known as heat pipes. Other cooling methods include but are not limited to the use of large conductive bodies able to store and displace heat in contact with a hot body such as a heat sink, the use of thin fins made of thermal conductors arranged along successive layers to increase the surface contact area between the heated surface and the colder air, the use of cross-flow heat-exchangers where a hot gas is transported along a first flow direction in thermal communication with a cold gas flowing in a second flow direction, the use of thermoelectric cooling where heat is transferred between successive layers of different materials once an electrical potential is created between the layers, and the use of a thermotunnel cooling method where electronic flux of electrons in a tunnel removes heat from surrounding atoms.
These cooling methods from the prior art, if used individually, can fail to address one or more of the problems of increased heat fluxes, limited encumbrance, limited convective air flow, reduced heating surfaces, and colder junction temperatures requirements. What is unknown and needed is an improved thermal management device, a circuit assembly equipped with an improved thermal management device, and a method of manufacture thereof.